The invention relates to optical communications networks, and more particularly relates to a protection ring architecture for such networks.
Optical transmission systems and, especially systems using Dense Wavelength Division Multiplexing (DWDM), are desirable since they provide extremely wide bandwidths for communications channels. Each DWDM transmission system carries a plurality of, for example, 16, 40 even 80, optical channels (wavelengths) on a single optical fiber and single optical repeater. However, there is a trade off between providing wider bandwidth communications channels, with their corresponding lower cost of transport, and their vulnerability to a large-scale disruption of communications services because of a transmission equipment and/or medium failure. It is, therefore, important that an optical transmission system, for example, those employing DWDM, have the capability to quickly recover from a transmission medium failure to prevent the failure from disrupting communications services.
Prior attempts at providing adequate restoration in optical transmission systems have focused on either so-called 1+1 optical protection switching or 0xc3x971 optical protection switching. The former type of protection switching is relatively expensive and less efficient when compared with the latter type. The reason for this is that in 1+1 optical protection switching the service traffic is transmitted simultaneously over both the service channel and corresponding protection channel. It appears that an optical transmission system typically provides either 1+1 optical protection switching or 0xc3x971 optical protection switching, but not both. Consequently, customer traffic using an optical transmission system to reach an intended recipient is locked into the type of protection switching provided by the transmission system, even if that type of protection switching is the more expensive 1+1 type.
The capabilities of prior optical systems are advanced in an optical communications system comprising a plurality of optical nodes interconnected in a conventional optical ring configuration using at least a pair of optical transmission media. The optical transmission media may be, for example, optical fiber. Specifically, in accordance with various aspects of the invention, the capabilities of an optical node are advanced to include a plurality of different transmission states involving one or more sources and to effect either 1+1 optical protection switching, 0xc3x971 optical protection switching, or span protection switching to recover from a optical transmission media failure. Moreover, in accordance with an aspect of the invention, sources/clients who respectively transport data over the same channel in different directions (east or west) in an optical ring may elect different (or the same) forms of protection switching. For example, a customer who""s data is transmitted upstream (westerly) may elect, for example, 1+1 protection, and the customer who""s data is transported downstream (easterly) may elect, for example, span protection (or 0xc3x971 protection). Further, if a protection channel for a given direction is not being used for 1+1 protection, then the channel may be used to transport xe2x80x9cpre-emptoryxe2x80x9d traffic/data on behalf of still another source. However, such traffic may be quickly removed from the protection channel if the channel is needed for xe2x80x9cbackupxe2x80x9d protection of a corresponding service channel. Further, in accordance with various aspects of the invention, such optical protection switching also includes xe2x80x9ckeep-alivexe2x80x9d and xe2x80x9cprotection accessxe2x80x9d states, as will be discussed below.
The foregoing is achieved using an efficient switching matrix characterized by a unique set of switching transmission and protection states including access without protection switching. In a shared configuration, protection capacity is provided for each service channel.